Picklists don't automatically populate with associated items?

Picklists don't automatically populate with associated items?

When we go to create a new picklist, we type in the item # of the main assembly item (which is a Composite Item), that has all the sub-items linked to it as associated items. The associated items do not automatically get added to the picklist- it's like we have to recreate the entire Composite Item. Am I missing something?